Liquid crystal cells for polarization rotation

ABSTRACT

An optical element comprising a stacked liquid crystal (LC) structure for rotating polarization (e.g., handedness) of an incident circularly polarized light over a broad wavelength and incident angle for head-mounted displays (HMD)s display application is proposed. The stacked LC structure has a dual cell structures, which includes at least a first LC cell and a second LC cell, and the stacked LC structure rotates the polarized light for a broad band of light (e.g., visible spectrum) over a given field a view. The performance of designed dual LC cells structures may be optimized for narrow band wavelength and a narrow incident angle for different application cases.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of provisional U.S. PatentApplication No. 62/507,723, filed May 17, 2017 and U.S. ProvisionalApplication No. 62/571,147, filed Oct. 11, 2017. The foregoingapplications are incorporated by reference herein.

BACKGROUND

The present disclosure generally relates to adaptive visual images fromelectronic displays, and specifically to minimizing the birefringentdispersion of birefringent optical components.

A near-eye display (NED), augmented reality (AR) headsets, and virtualreality (VR) headsets can be used to simulate virtual, augmented, andmixed reality environments. For example, stereoscopic images can bedisplayed on an electronic display inside the headset to simulate theillusion of depth. Head tracking sensors can be used to estimate whatportion of the virtual environment is being viewed by the user. Such asimulation, however, can cause visual fatigue and nausea resulting froman inability of existing headsets to correctly render or otherwisecompensate for vergence and accommodation conflicts.

To create a comfortable viewing experience, the virtual image generatedby the headset needs to be generated at the right distance from the eye.One or more optical components such as liquid crystal cells may be usedto achieve this. However, conventional liquid crystal displays arebirefringent.

SUMMARY

A stacked liquid crystal (LC) integrated into a display of a near-eyedisplay (NED) is presented herein. The NED may be part of an artificialreality system. The stacked LC structure may be used as a polarizationrotator. Here the stacked LC structure includes one or more transparentsubstrates and two LC cells (e.g., film type). Broadband light incidenton a stacked LC structure exits the stacked LC structure as broadbandlight after propagating through the one or more substrates and the twoLC cells. The stacked LC structure is configured to rotate apolarization of the incident broadband light. That is, the incidentbroadband light exits the stacked LC structure as a broadband lightwhose polarization has been rotated relative to a polarization of theincident broadband light. For example, the incident broadband light isright hand circularly polarized (RCP) while the broadband light exitingthe stacked LC structure is left hand circularly polarized (LCP). In anembodiment, one of the two LC cells comprising the stacked LC structureis driven with an external power supply to change the total phaseretardation of the stacked LC structure while the other LC cell is usedas a compensator. In some embodiments, the other LC cell may also act asa backup LC cell for driving the system. In some embodiments, both LCcells are driven with an external power supply to change the total phaseretardation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a near-eye display (NED), in accordance with anembodiment.

FIG. 2 is a cross-section of an eyewear of the NED in FIG. 1, inaccordance with an embodiment.

FIG. 3 is a design of a stacked LC structure that includes two LC cellsconfigured as Pi Cells, in accordance with an embodiment.

FIG. 4A is a design of a stacked LC cell structure that includes two LCcells with antiparallel alignment, in accordance with an embodiment.

FIG. 4B is the design of a stacked LC cell structure depicted in FIG. 4Ain an alternate configuration, in accordance with an embodiment.

FIG. 5A is a design of a stacked LC cell structure that includes two LCcells with perpendicular alignment, in accordance with an embodiment.

FIG. 5B is the design of a stacked LC structure depicted in FIG. 5A inan alternate configuration, in accordance with an embodiment.

FIG. 6 a block diagram of a system environment that includes the NEDshown in FIG. 1, in accordance with an embodiment.

FIG. 7 is an isometric view of a stacked LC structure comprising LCcells in a twist angle configuration, in accordance with an embodiment.

FIG. 8 is a design example of a stacked LC structure comprising two LCcells each of which is in a twisted nematic configuration and includesbiaxial compensation films, in accordance with an embodiment.

FIG. 9 is an isometric view of a stacked LC structure comprising two LCcells in a twisted nematic configuration and includes plastic filmsubstrates, in accordance with an embodiment.

FIG. 10 is an isometric view of a stacked LC structure comprising two LCcells in a twisted nematic configuration with plastic film substratesand compensated with biaxial compensation films, in accordance with anembodiment.

The figures depict embodiments of the present disclosure for purposes ofillustration only. One skilled in the art will readily recognize fromthe following description that alternative embodiments of the structuresand methods illustrated herein may be employed without departing fromthe principles, or benefits touted, of the disclosure described herein.

DETAILED DESCRIPTION

Embodiments of the invention may include or be implemented inconjunction with an artificial reality system. Artificial reality is aform of reality that has been adjusted in some manner beforepresentation to a user, which may include, e.g., a virtual reality (VR),an augmented reality (AR), a mixed reality (MR), a hybrid reality, orsome combination and/or derivatives thereof. Artificial reality contentmay include completely generated content or generated content combinedwith captured (e.g., real-world) content. The artificial reality contentmay include video, audio, haptic feedback, or some combination thereof,and any of which may be presented in a single channel or in multiplechannels (such as stereo video that produces a three-dimensional effectto the viewer). Additionally, in some embodiments, artificial realitymay also be associated with applications, products, accessories,services, or some combination thereof, that are used to, e.g., createcontent in an artificial reality and/or are otherwise used in (e.g.,perform activities in) an artificial reality. The artificial realitysystem that provides the artificial reality content may be implementedon various platforms, including a head-mounted display (HMD) connectedto a host computer system, a standalone HMD, a mobile device orcomputing system, or any other hardware platform capable of providingartificial reality content to one or more viewers.

Configuration Overview

A near eye display (NED) includes one or more display assemblies (e.g.,one for each lens) configured to apply an amount of phase adjustment toa polarization of a broadband light as it propagates through the displayassemblies. The amount of phase adjustment is such a polarization of thebroadband light is rotated. In an embodiment, the display assemblyincludes two liquid crystal (LC) cells arranged into a stacked LCstructure. As broadband light passes through each of the plurality of LCcells, each LC cell applies an amount of phase adjustment to apolarization of the broadband light. As used herein, phase adjustmentrefers to a change in a phase shift between polarization vectorcomponents of light and/or a rotation of polarization vector components.Note that the phase shift may be zero, and the change in phase shift maybe to make it non-zero or vice versa. Accordingly, the amount of phaseadjustment may cause, e.g., rotation of linear polarized light (e.g.,rotates by 90 degrees), a change in handedness for circularly polarizedlight (e.g., right to left or vice versa), etc. In some embodiments, thetotal amount of phase adjustment acts to rotate the polarization of thebroadband light (e.g., rotate linear polarized light by some amount).Broadband light may include, e.g., the entire visible spectrum. In someembodiments, the display assembly adjusts the amount of phase adjustmentapplied to a polarization of the broad band light in accordance withinstructions from the NED to, for example, to mitigate vergenceaccommodation conflict of the eyes of a user.

In an embodiment, each stacked LC structure includes two LC cells suchthat the two LC cells have an antiparallel or a perpendicular alignmentto one another. The LC cells within a stacked LC cell structure may bein an active or a passive state and are configured to contribute someamount of phase adjustment to light emitted by the display assembly. Insome embodiments, each of the plurality of LC structures additionallycomprises one or more polarization rotators. The propagation of lightthrough a first LC cell in the stacked LC structure may result in theformation of a ghost image. The stacked LC structure is configured suchthat the light exiting the first LC cell propagates through a second LCcell. The alignment of the second LC cell with respect to the first LCcell reduces a field of view of the ghost image. In one or moreembodiments, the field of view of the stacked LC structure is a range of60 to 120 degrees. Accordingly, the stacked LC structure is wavelengthindependent for a range of wavelengths inclusive of the broadband lightover a broad range of incident angle.

FIG. 1 is a diagram of a NED 100, in accordance with an embodiment. TheNED 100 presents media to a user. Examples of media presented by the NED100 include one or more images, video, audio, or some combinationthereof In some embodiments, audio is presented via an external device(e.g., speakers and/or headphones) that receives audio information fromthe NED 100, a console (not shown), or both, and presents audio databased on the audio information. The NED 100 is generally configured tooperate as an artificial reality NED. In some embodiments, the NED 100may augment views of a physical, real-world environment withcomputer-generated elements (e.g., images, video, sound, etc.).

The NED 100 shown in FIG. 1 includes a frame 105 and a display 110. Theframe 105 includes one or more optical elements which together displaymedia to users. The display 110 is configured for users to see thecontent presented by the NED 100. The display 110 receives image lightfrom a local area being viewed by a user. In an embodiment the display110 includes one or more optical elements configured to adjust the fieldof view and adjust the accommodation. The display 110 is furtherdescribed below in conjunction with FIG. 2. In some embodiments, the NED100 may also be referred to as a HMD.

FIG. 2 is a cross section 200 of an eyewear of the NED 100 illustratedin FIG. 1, in accordance with an embodiment. The cross section 200includes at least one display assembly 210 integrated into the display110, and an exit pupil 220. The exit pupil 220 is a location where aneye 230 is positioned when a user wears the NED 100. In someembodiments, the frame 105 may represent a frame of eye-wear glasses.For purposes of illustration, FIG. 2 shows the cross section 200associated with a single eye 230 and a single display assembly 210, butin alternative embodiments not shown, another display assembly which isseparate from the display assembly 210 shown in FIG. 2, provides imagelight to another eye 230 of the user.

The display assembly 210 is configured to direct the image light to theeye 230 through the exit pupil 220. In some embodiments, when the NED100 is configured as an AR NED, the display assembly 210 also directslight from a local area surrounding the NED 100 to the eye 230 throughthe exit pupil 220. The display assembly 210 may be configured to emitimage light at a particular focal distance in accordance with varifocalinstructions, e.g., provided from a varifocal module (not shown in FIG.2). The varifocal module may include one or more LC lenses and be partof an HMD as described in U.S. application Ser. No. 15/693,839, filedSep. 1, 2017, which is incorporated by reference in its entirety herein.The varifocal module may also be used in other HMDs and/or otherapplications where polarization of light is rotated over a broadwavelength range and over a broad range of incident angles.

The display assembly 210 may be composed of one or more materials (e.g.,plastic, glass, etc.) with one or more refractive indices thateffectively minimize the weight and widen a field of view of the NED100. In alternate configurations, the NED 100 includes one or moreoptical elements between the display assembly 210 and the eye 230. Theoptical elements may act to, e.g., correct aberrations in image lightemitted from the display assembly 210, magnify image light, perform someother optical adjustment of image light emitted from the displayassembly 210, or some combination thereof. The example for opticalelements may include an aperture, a Fresnel lens, a convex lens, aconcave lens, a diffractive element, a waveguide, a filter, a polarizer,a diffuser, a fiber taper, one or more reflective surfaces, a polarizingreflective surface, a birefringent element, or any other suitableoptical element that affects image light emitted from the displayassembly 210. In still further embodiments, the display assembly 210additionally includes liquid crystal lenses including one or morestacked LC structures configured to perform an amount of phaseadjustment such that, in the aggregate, the one or more stacked LCstructures act to rotate a polarization based on an applied voltage.

Liquid crystal lenses comprise liquid crystals (LCs) arranged into astacked LC structure. A LC cell may be, e.g., a film type LC cell, athin-glass type LC cell. An optical mode of the stacked LC structure maybe one of an electrically controlled birefringence (ECB) mode, avertical aligned (VA) mode), a multiple-domain vertical aligned (MVA)mode, a twisted nematic (TN) mode, a super twisted nematic (STN) mode,and an optical compensated (OCB) mode. Details of stacked LC structuresare discussed in detail below in conjunction with FIGS. 3-5B. Somespecific design examples of stacked LC structures comprising LC cells,including example material properties, are described below inconjunction with FIGS. 7-10.

The stacked LC structure includes a plurality of LC cells that arecoupled together in a manner such that an overall amount of phaseadjustment to light by the stacked LC structure is tunable. Theplurality of LC cells in the stacked LC structure may be active,passive, or some combination thereof. In some embodiments, at least oneof the plurality of LC cells is a nematic LC cell, a nematic LC cellwith chiral dopants, a chiral LC cell, a uniform lying helix (ULH) LCcell, a ferroelectric LC cell. In other embodiments, the LC cell is anelectrically drivable birefringence materials. The phase adjustment ofthe polarization of light as it propagates through the stacked LCstructure may accomplished by controlling the handedness of thepolarized light as it moves through the stacked LC structure. In anembodiment, the handedness of polarized light may be controlled via avoltage applied to the plurality of LC cells in the stacked LCstructure. In some embodiments, each LC cell within a stacked LCstructure is aligned to be perpendicular to an adjacent film type LCcell. In a perpendicular alignment, the average molecular alignment ofadjacent LC cells are configured to be orthogonal to one another. Inother embodiments, each film type LC cell has an antiparallel alignmentto an adjacent LC cell. In an antiparallel alignment, both a first LCand a second LC cell run parallel to one another but with oppositeoptical alignments. That is, in an antiparallel alignment, the averagemolecular alignment of the first LC cell is configured to beantiparallel to that of the second LC cell. In still other embodiments,the stacked LC structure comprises a single LC cell with a compensationlayer. The embodiments described above are described in detail below inconjunction with FIGS. 3-5B and FIGS. 8A-11B.

In some embodiments, the NED 100 further includes an eye tracker (notshown in FIG. 2) for determining and tracking a position of the eye 230,i.e., an angle and orientation of eye-gaze. Note that information aboutthe position of the eye 230 also includes information about anorientation of the eye 230, i.e., information about user's eye-gaze.Based on the determined and tracked position and orientation of the eye230, the NED 100 adjusts image light emitted from the display assembly210. In some embodiments, the NED 100 adjusts focus of the image lightand ensures that the image light is in focus at the determined angle ofeye-gaze in order to mitigate the vergence-accommodation conflict.Additionally, or alternatively, the NED 100 adjusts resolution of theimage light by performing foveated rendering of the image light, basedon the position of the eye 230. Additionally, or alternatively, the NED100 uses the information on a gaze position and orientation to providecontextual awareness for the user's attention, whether on real orvirtual content. The eye tracker generally includes an illuminationsource and an imaging device (camera). In some embodiments, componentsof the eye tracker are integrated into the display assembly 210. Inalternate embodiments, components of the eye tracker are integrated intothe frame 105.

Example Stacked LC Structures

Below various designs of stacked LC structures are discussed. Thestacked LC structures in the examples below are configured aspolarization rotators of an image of a local area being imaged by theNED 100. In the embodiments discussed below in conjunction with FIGS.3-5, the stacked LC structure may additionally or alternatively beconfigured as a switchable waveplate responsive to an applied voltage.It should be noted that in one or more embodiments, the field of view ofthe various stacked LC structures is between 60 to 120 degrees. It isimportant to note that these designs are merely illustrative, and otherdesigns of stacked structures may be generated using the principlesdescribed herein.

FIG. 3 is a design of a stacked LC structure 300 that includes two LCcells 305 a and 305 b configured as Pi Cells, in accordance with anembodiment. The stacked LC structure 300 comprises two LC cells (e.g.,LC cell 305 a and LC cell 305 b), a bottom substrate 310 a, and topsubstrate 330 a. The LC cell 305 a and LC cell 305 b are opticallyisotropic colloidal systems in which the dispersive medium is a highlystructured liquid that is sensitive to e.g., electric and magneticfields. The LC cells 305 a and 305 b each suspend a plurality of LCmolecules 320. In various example embodiments, each of the LC cell 305 aand LC cell 305 are approximately 100 nanometers (nm) to 500 nm thick.We note that the thickness of the LC cell is may vary based on, e.g., anindex of refraction of the liquid crystal.

The LC cells 305 a and 305 b are both stabilized into a Pi state. Thatis, the plurality of LC molecules 320 encapsulated within the LC cells305 a and 305 b are configured to form Pi cells. Pi cells are generallyused in applications requiring fast response times and increased viewingangle (e.g., large screen televisions and high speed optical shutters).In the LC cells 305 a and 305 b, the plurality of LC molecules 320 has a180° twist angle. Each of the plurality of LC molecules 320 areelongated, rod-like organic molecules with a dipole moment along theaxis of the molecule. In one or more embodiments, each of the pluralityof LC molecules 320 have a size of a few nanometers and comprise bothrigid and flexible parts allowing for orientational and positionalorder. In an embodiment, the plurality of LC molecules may exhibitoptical birefringence depending on external conditions such as anexternal field (e.g., an applied voltage). Generally, in a Pi Cell, whenthe electric field is switched off (e.g., the application of 0 V) the LCmolecules 320 experience a torque which causes an electro-opticalresponse of the Pi Cell. Thus, the modulation of an external field to aLC cell (e.g., LC cell 305 a or LC cell 305 b) may result inmodification of the optical birefringence of that LC cell.

Each of the LC cells 305 a and 305 b are between two opticallytransparent electrodes. The top substrates 330 a and 330 b and bottomsubstrates 310 a and 310 b comprise a glass substrate coated with anoptically transparent electrically conductive polymer. In otherembodiments, the substrates 330 a and 330 b are an optically transparentplastic coated with an electrically conductive polymer. In an exampleembodiment, the optically transparent electrically conductive polymer isindium tin oxide (ITO). In this embodiment, the substrates 310 a and 310b are isotropic and do not affect the polarization of broadband light asit passes through the substrate. The top substrates 330 a and 330 b andthe bottom substrates 310 a and 310 b are configured to apply a uniformelectric field through the LC cells 305 a and 305 b, respectively. InFIG. 3, the LC cell 305 a is coupled to the top substrate 330 a and thebottom substrate 310 a. Similarly, in FIG. 3, the LC cell 305 b iscoupled to a top substrate 330 b and bottom substrate 310 a. Here, theLC cell 305 a and LC cell 305 b are configured such that one of thecells is configured to drive the stacked LC structure 300 (i.e., controlits total phase retardation) while the other is configured as acompensator or backup in the event that a failure is detected. Invarious embodiments, each of the top substrates 330 a and 330 b and thebottom substrates 310 a and 310 b are further coupled to a controller(not shown) configured to apply a voltage to one or more of the topsubstrates 330 a and 330 b. Here, the application of a voltage causesthe formation of an electric field through one or more of the LC cell305 a and LC cell 305 b. In various embodiments, the generated electricfield is proportional to the applied voltage. In still otherembodiments, the controller is configured to determine a failure in oneof the LC cells (e.g., LC cell 305 a or LC cell 305 b) and adjust thevoltage applied accordingly. For example, if a failure is detected in LCcell 305 a, the controller may apply a voltage to LC cell 305 b suchthat it drives the total phase retardation of the stacked LC structure300.

Turning now to the propagation of light through the stacked LC structure300, in FIG. 3, light 340 is incident on the bottom substrate 310 a. Thelight 340 is transmitted into the LC cell 305A via the bottom substrate310 a. As the light 340 propagates through the LC cell 305 a,polarizations of the light 340 corresponding to the ordinary andextraordinary axis of the LC cell 305 a take different paths through theLC cell 305 a. And an amount of phase adjustment occurs based at leastin part on the ordinary and extraordinary axis having different indicesof refraction. Thus, the LC cell 305 a applies a first amount of phaseadjustment to the light 340 as it propagates through the LC cell 305 a.The light 305 is transmitted into the LC cell 305 b via the topsubstrate 330 a and top substrate 330 b. The LC cell 305 b is configuredto apply a second amount of phase adjustment to the light 340. The light340 exits the stacked LC structure 300, via the bottom substrate 310 b,as a light 350. The light 350 is light 340 after its phase is adjustedby a third amount wherein the third amount is not equal to a linearcombination of the first amount and the second amount. That is, thestacked LC structure 300 depicted in conjunction with FIG. 3 isconfigured to apply a third amount of phase adjustment to the light 340.In an example embodiment, the light 350 is RCP, LCP, horizontallylinearly polarized, vertically lineally polarized, or any combinationthereof. For example, a third amount of phase adjustment results in thelight 350 being RCP while the light 340 is LCP. In an exampleembodiment, as the light 305 propagates through the LC cell 305 a, theLC cell 305 a generates the desired image and an associated ghost imagedue to the birefringence of the LC cell 305 a. In the previous exampleembodiment, the LC cell 305 b is configured such that its birefringenceis orthogonal to that of the first cell. That is, the birefringence ofthe LC cell 305 b is such that it negates the birefringence of the LCcell 305 a, thus reducing the field of view of the ghost image. Itshould be noted that two LC cells (e.g., LC cell 305 a and LC cell 305b) need to be configured such that the birefringence of one balancesthat of the other. In one embodiment, the LC cells 305 a and 305 b areconfigured such that both LC cell 305 a and LC cell 305 b are identicaland are oriented such that the average molecular alignment of LC cell305 a and 305 a are orthogonal to one another. Alternatively, the LCcells 305 a and 305 b may be configured such they are oriented to beantiparallel to one another. In still other embodiments, the stacked LCstructure 300 may comprise two or more LC cells as long as the two ormore LC cells are configured to compensate for the other LC cells. Thetotal phase retardation of the stacked LC structure 300 is a quarterwaveplate, a half waveplate, or a one-waveplate. Here, the total phaseretardation of the stacked LC structure 300 may be controllable throughthe application of a voltage to one a LC cell (e.g., LC cell 305 a).

FIG. 4A is a design of a stacked LC cell structure 300, in accordancewith an embodiment. The stacked LC cell structure 400 comprises a LCcell 405 a, a LC cell 405 b, two bottom substrates 410 a and 410 b, andtwo top substrates 430 a and 430 b. In FIG. 4A, the LC cells 405 a and405 b are embodiments of LC cells 305 a and 305 b; top substrates 430 aand 430 b are embodiments of top substrates 330 a and 330 b; and bottomsubstrates 410 a and 410 b are embodiments of bottom substrates of 310 aand 310 b. The LC cells 305 a and 305 b, the bottom substrates 310 a and310 b, and top substrates 330 a and 330 b are described in detail,above, in conjunction with FIG. 3.

Each of the LC cells 405 a and 405 b comprises a plurality of LCmolecules 420. The plurality of LC molecules 420 are an embodiment of LCmolecules 320 described in detail, above, in conjunction with FIG. 3. InFIG. 4A, each of the plurality of LC molecules 420 are oriented suchthat the dipole moment of the LC molecule is at ˜3° in the X-Z plane.The LC cell 405 a is between the top substrate 410 a and the topsubstrate 430 a. Similarly, the LC cell 405 b is between the topsubstrate 430 b and bottom substrate 410 b. In one or more embodiments,the bottom substrate 410 a and the top substrate 430 a are configured togenerate an electric field of a first polarization across the LC cell405 a; and the top substrate 430 b and bottom substrate 410 b areconfigured to generate an electric field across the LC cell 405 a with asecond polarization that is opposite that of the first polarization.

The bottom substrate 410 a is coupled to the LC cell 405 a and the topsubstrate 430 a is coupled to both the LC cell 405 a and the topsubstrate 430 b. Light 440 is an embodiment of light 340 and is incidenton the bottom substrate 410 a. The light 440 is transmitted into the LCcell 405A via the bottom substrate 410 a. As the light 440 propagatesthrough the LC cell 405 a, different polarization components of thelight 440 are affected differently by the ordinary and extraordinaryaxis of the LC cell 405 a, and take different paths through the LC cell405 a. Thus, the LC cell 405 a applies a first amount of phaseadjustment to the light 440. The light 440 is transmitted into the LCcell 405 b from the LC cell 405 a via the top substrate 430 a and thetop substrate 430 b. The LC cell 405 b is located between the topsubstrate 430 b and the bottom substrate 410 b. The LC cell 405 b isconfigured to apply a second amount of phase adjustment to the light 440as it propagates through it. The light 440 exits the stacked LCstructure 400, via the bottom substrate 410 b, as a light 450. Thestacked LC structure 400 is configured to impart a third amount of phaseadjustment to the broadband light as it propagates through the LCstructure 400. Here, the third amount of phase adjustment is not alinear combination of the first amount of phase adjustment and thesecond amount of phase adjustment. In other embodiments, the LC cell 405b is utilized as a backup cell for driving the system. For example, inembodiments in which the LC cell 405 a is used to drive the total phaseretardation of the stacked LC structure 400 and a failure is detected inLC cell 405 a, the LC cell 405 b is operated as the driving cellinstead.

FIG. 4B is a design of a stacked LC structure 400 depicted in FIG. 4A inan alternate configuration. That is, the stacked LC structure 400 inFIG. 4B is configured to be antiparallel to that depicted in conjunctionwith FIG. 4A. In an embodiment, the top substrate 430 a and the bottomsubstrate 410 a are configured to generate an electric field of a firstpolarization across the LC cell 405 a, and the bottom substrate 410 band the top substrate 430 b are configured to generate an electric fieldof a second polarization across the LC cell 405 b and the secondpolarization is opposite that of the first polarization.

In FIG. 4B, the light 440 is incident upon the top substrate 430 a andpropagates through the LC cell 405 a and into the LC cell 405 b via thebottom substrate 410 a and the bottom substrate 410 b. The light 440exits the stacked LC structure 400 as a light 450 via the bottomsubstrate 410 a. The stacked LC structure 400 depicted in conjunctionwith FIG. 4B is configured to apply a third amount of phase adjustmentto the polarization of the light 440 propagating through it. That is, apolarization of the light 450 is that of light 440 changed by a thirdamount of phase adjustment, representative of a total phase adjustmentcaused by the stacked LC structure 400. And the total amount of phaseadjustment is such that polarization of light 450 may be rotatedrelative to the light 440. Here, the third amount of phase adjustment isnot a linear combination of the first amount of phase adjustment and thesecond amount of phase adjustment associated with LC Cells 405 a and 405b, respectively.

FIG. 5A is a design of a stacked LC cell structure 500 that includes twoLC cells 505 a and 505 b with perpendicular alignment, in accordancewith an embodiment. The stacked LC cell structure 500 comprises a LCcell 505 a, a LC cell 505 b, two bottom substrates 510 a and 510 b, andtwo top substrates 530 a and 530 b. In a perpendicular alignment, theaverage molecular alignment of the LC cell 505 a is orthogonal to thatof the LC 505 b. In FIG. 5A, the LC cells 505 a and 505 b areembodiments of LC cells 305 a and 305 b, top substrates 530 a and 530 bare embodiments of top substrates 330 a and 330 b, and bottom substrates510 a and 510 b are embodiments of bottom substrates of 310 a and 310 b.The LC cells 305 a and 305 b, the bottom substrates 310 a and 310 b, andtop substrates 330 a and 330 b are described in detail, above, inconjunction with FIG. 3.

Both of the LC cells 505 a and 505 b comprise a plurality of LCmolecules 520. The plurality of LC molecules 520 are an embodiment ofthe LC molecules 320 described in detail above in conjunction with FIG.3. Each of the plurality of LC molecules 520 associated with the LC cell505 a are oriented such their dipole moment are parallel to the y axis.On the other hand, the plurality of LC modules 520 associated with theLC cell 505 b are oriented such that their dipole moment is in a rangebetween 0.5° and 89.5° to the X-Z plane, in the absence of an electricfield. In some embodiments, the plurality of LC molecules 520 make anangle in the range of 0.5° to 10° to the X-Z plane in embodiments wherethe LC cells 505 a and 505 b have a positive dielectric anisotropy. Insome embodiments, the plurality of LC molecules 520 make an angle in therange of 80° to 89.5° to the X-Z plane in embodiments where the LC cells505 a and 505 b have a negative dielectric anisotropy. A birefringenceof each of the plurality of LC molecules 520 is an intrinsic property ofa LC molecule associated with the plurality of LC molecules 520. Thatis, a birefringence of a LC molecule of the plurality of LC molecules520 is not related to its orientation. In various embodiments, a phaseretardation experienced by a light propagating through a LC cell (e.g.,LC cell 505 a and 505 b) is related to the orientation of the pluralityof the LC molecules. For example, in embodiments including an LC cell505 a and 505 b with a positive dielectric anisotropy, the retardationdecreases with an increased tilt angle. In some other embodimentsincluding a LC cell 505 a and 505 b with a negative dielectricanisotropy, the phase retardation experienced by a light passing throughthe LC cell 505 a and 505 b increases with a decreased tilt angle. TheLC cell 505 a is between the top substrate 530 a and bottom substrate510 a such that the top substrate 530 a and bottom substrate 510 a areconfigured to apply an electric field across the LC cell 505 a. Here,the bottom substrate 510 a is coupled to the bottom substrate 510 b. TheLC cell 505 b is between the top substrate 530 b and the bottomsubstrate 510 b such that an electric field applied to the LC cell 505 bis oriented antiparallel to the electric field applied to the LC cell505 a.

In FIG. 5A, the top substrate 530 a is coupled to the LC cell 505 a andthe bottom substrate 510 a is coupled to both the LC cell 405 a and thetop substrate 530 b. A light 540 is an embodiment of the light 340 andis incident on the top substrate 530 a. The light 540 is transmittedinto the LC cell 505A via the top substrate 530 a. As the light 540propagates through the LC cell 505 a, polarization of the light 540corresponding to the ordinary and extraordinary axis of the LC cell 505a take different paths through the LC cell 505 a. Thus, the LC cell 505a changes the polarization of the light 540 as it propagates through theLC cell 505 a. The light 540 is transmitted into the LC cell 505 b fromthe LC cell 505 a via the top substrate 530 a and the bottom substrate510 a. The LC cell 505 b is between the top substrate 530 b and thebottom substrate 510 b and is configured to change the polarization ofthe light 540 by a second amount as it propagates trough the LC cell 505b. The light 540 exits the stacked LC structure 500, via the bottomsubstrate 510 b, as a light 550. The light 550 is light 540 whosepolarization is changed by a third amount of phase adjustment,representative of a total phase adjustment caused by the stacked LCstructure 500. And the total amount of phase adjustment is such thatpolarization of light 550 may be rotated relative to the light 540. Notethat the third amount of phase adjustment is not a linear combination ofthe first amount of phase adjustment and the second amount of phaseadjustment. In other embodiments, the LC cell 505 b is utilized as abackup cell for driving the system. For example, in embodiments in whichthe LC cell 505 a is used to drive the total phase retardation of thestacked LC structure 500 and a failure is detected in LC cell 505 a, theLC cell 505 b is operated as the driving cell instead.

FIG. 5B is the design of a stacked liquid crystal structure 500 depictedin FIG. 5A in an alternate configuration, in accordance with anembodiment. That is, the stacked LC structure 500 in FIG. 5A isconfigured to be perpendicular to that depicted in conjunction with FIG.5A. In an embodiment, the bottom substrate 510 a and the top substrate530 a are configured to generate a uniform electric field orientedantiparallel to the z axis through the LC cell 505 a; and the bottomsubstrate 510 b and the top substrate 530 b are configured to generate auniform electric through the LC cell 505 b such that the electric fieldis oriented antiparallel to the electric field through the LC cell 505a.

In FIG. 5B, the light 540 is incident upon the top substrate 530 a andpropagates through the LC cell 505 a and into the LC cell 505 b via thebottom substrate 510 a and the top substrate 530 b. The light 540 exitsthe stacked LC structure 500 as light 550 via the bottom substrate 510b. In various embodiments, the light 550 is light 540 whose polarizationis changed by a third amount of phase adjustment, representative of atotal phase adjustment caused by the stacked LC structure 500. And thetotal amount of phase adjustment is such that polarization of light 550may be rotated relative to the light 540. Note that the third amount ofphase adjustment is not a linear combination of a first amount and asecond amount of phase adjustment associated with the LC Cell 505 a and505 b, respectively.

Additionally, performance of a stacked LC structure (e.g., stacked LCstructure 300, stacked LC structure 400, and stacked LC structure 500)may be improved through the application of one or more compensationlayers to the LC cells. For example, one or more compensation layers maybe used to increase a range of wavelengths over which the amount ofphase adjustment caused by one or more stacked LC structures iswavelength independent. Generally, the compensation layer is amultilayer birefringence film. For example, each of the one or morecompensation layers provide one of a c-plate compensation, uniaxiala-plate compensation, and negative birefringent film compensation. Instill other embodiments, the compensation layer may provide negativeo-plate, positive o-plate, and liquid crystal compensation (LCC)compensation.

System Environment

FIG. 6 is a block diagram of one embodiment of a NED system 600 in whicha console 605 operates. The NED system 600 may operate in an artificialreality environment. The NED system 600 shown by FIG. 6 comprises a NED610 and an input/output (I/O) interface 620 that is coupled to theconsole 605. While FIG. 6 shows an example NED system 600 including oneNEDs 610 and on I/O interface 615, in other embodiments any number ofthese components may be included in the NED system 600. For example,there may be multiple NEDs 610 each having an associated I/O interface615, with each NED 610 and I/O interface 615 communicating with theconsole 605. In alternative configurations, different and/or additionalcomponents may be included in the NED system 600. Additionally,functionality described in conjunction with one or more of thecomponents shown in FIG. 6 may be distributed among the components in adifferent manner than described in conjunction with FIG. 6 in someembodiments. For example, some or all of the functionality of theconsole 605 is provided by the NED 610.

The NED 610 is a near-eye display (also referred to as a head-mounteddisplay) that presents content to a user comprising virtual and/oraugmented views of a physical, real-world environment withcomputer-generated elements (e.g., two-dimensional or three-dimensionalimages, two-dimensional or three-dimensional video, sound, etc.). Insome embodiments, the presented content includes audio that is presentedvia an external device (e.g., speakers and/or headphones) that receivesaudio information from the NED 610, the console 605, or both, andpresents audio data based on the audio information. The NED 610 includesan optical assembly 620, a depth camera assembly (DCA) 625, display 630,eye tracking system 616, multifocal block 640. Some embodiments of theNED 610 have different components than those described in conjunctionwith FIG. 6. Additionally, the functionality provided by variouscomponents described in conjunction with FIG. 6 may be differentlydistributed among the components of the NED 610 in other embodiments. Anembodiment of the NED 610 is the NED 100 described above in conjunctionwith FIG. 1.

The optical assembly 620 magnifies image light received from the display630, corrects optical errors associated with the image light, andpresents the corrected image light to a user of the NED 610. The opticalassembly 620 includes a plurality of optical elements. Example opticalelements included in the optical assembly 620 include: an aperture, aFresnel lens, a convex lens, a concave lens, a filter, a reflectingsurface, or any other suitable optical element that affects image light.Moreover, the optical assembly 620 may include combinations of differentoptical elements. Optical elements may also include switchablewaveplates formed through the use of one or more stacked LC structures(e.g., stacked LC structures 300, 400, and 500). Examples of opticalelements including stacked LC structures include quarter waveplates,half waveplates, and full waveplate. In some embodiments, one or more ofthe optical elements in the optical assembly 620 may have one or morecoatings, such as partially reflective or anti-reflective coatings.

The DCA 625 captures data describing depth information of an areasurrounding the NED 610. The DCA 625 may determine depth informationbased on one or more of a structured light emitter, time of flightcamera, or some combination thereof. The DCA 625 can compute the depthinformation using the data, or the DCA 625 can send this information toanother device such as the console 605 that can determine the depthinformation using data from the DCA 625.

The DCA 625 includes an illumination source, an imaging device, and acontroller. The illumination source emits light to track the user's eye.In an embodiment, the emitted light is a structured light. Theillumination source includes a plurality of emitters that each emitslight having certain characteristics (e.g., wavelength, polarization,coherence, temporal behavior, etc.). The characteristics may be the sameor different between emitters, and the emitters can be operatedsimultaneously or individually. In one embodiment, the plurality ofemitters could be, e.g., laser diodes (e.g., edge emitters), inorganicor organic light-emitting diodes (LEDs), a vertical-cavitysurface-emitting laser (VCSEL), or some other source. In someembodiments, a single emitter or a plurality of emitters in theillumination source can emit light having a structured light pattern.The imaging device captures ambient light and light from one or moreemitters of the plurality of emitters of the plurality of emitters thatis reflected from objects in the area. The imaging device may be aninfrared camera, or a camera configured to operate in a visiblespectrum. The controller coordinates how the illumination source emitslight and how the imaging device captures light in order to determinethe distance between the user and various objects in a local areasurrounding the NED 610. In some embodiments, the controller alsodetermines depth information associated with the local area using thecaptured images.

The display 630 displays two-dimensional or three-dimensional images tothe user in accordance with data received from the console 605. Invarious embodiments, the display 630 comprises a single display ormultiple displays (e.g., a display for each eye of a user). In someembodiments, the display 630 comprises a single or multiple waveguidedisplays. Light can be coupled into the single or multiple waveguidedisplays via, e.g., a liquid crystal display (LCD), an organic lightemitting diode (OLED) display, an inorganic light emitting diode (ILED)display, an active-matrix organic light-emitting diode (AMOLED) display,a transparent organic light emitting diode (TOLED) display, alaser-based display, one or more waveguides, some other display, ascanner, one-dimensional array, or some combination thereof. Anembodiment the display 630 is a waveguide-based display assemblyconfigured to render information (i.e., pictures, text, and video) suchthat it appears at a location in the local area associated with anobject in the local area as determined by the DCA 625.

In some embodiments, the optical assembly 620 may be, additionally,configured to correct one or more types of optical error. Examples ofoptical error include barrel or pincushion distortions, longitudinalchromatic aberrations, or transverse chromatic aberrations. Other typesof optical errors may further include spherical aberrations, chromaticaberrations, or errors due to the lens field curvature, astigmatisms, orany other type of optical error. In some embodiments, content providedto the display 630 for display is pre-distorted, and the opticalassembly 620 corrects the distortion when it receives image light fromthe display 630 generated based on the content.

The eye tracking system 635 is integrated into the NED 610. The eyetracking system 635 determines eye tracking information associated withan eye of a user wearing the NED 610. The eye tracking informationdetermined by the eye tracking system 635 may comprise information abouta position of the user's eye, i.e., information about an angle of aneye-gaze. Alternatively, or additionally, the eye-tracking system 635may comprise one or more illumination sources and an imaging device(camera) directed towards the eye and is configured to determine avergence depth of a user's gaze based on the gaze point or an estimatedintersection of the gaze lines determined by the one or moreillumination sources associated with the eye tracking system 635.Vergence is the simultaneous movement or rotation of both eyes inopposite directions to maintain single binocular vision, which isnaturally and automatically performed by the human eye. Thus, a locationwhere a user's eyes are verged is where the user is looking and is alsotypically the location where the user's eyes are focused. For example,the eye tracking system 635 triangulates the gaze lines to estimate adistance or depth from the user associated with intersection of the gazelines. The depth associated with intersection of the gaze lines can thenbe used as an approximation for the accommodation distance, whichidentifies a distance from the user where the user's eyes are directed.Thus, the vergence distance allows determination of a location where theuser's eyes should be focused.

The multifocal block 640 activates or deactivates one or more SHWPs, oneor more stacked LC structures, or some combination thereof to adjust thefocal length (i.e., adjust the optical power) of the multifocal block640. In various embodiments, the multifocal block 640 adjusts its focallength responsive to one or more instructions from the console 605 basedon information about the local scene received from the DCA 625.

The multifocal block 640 is coupled to the eye tracking system 635 toobtain eye tracking information determined by the eye tracking system635. The multifocal block 640 may be configured to adjust focus of imagelight emitted from the display 630, based on the determined eye trackinginformation obtained from the eye tracking system 635. In this way, themultifocal block 640 can mitigate vergence-accommodation conflict inrelation to the image light. The multifocal block 640 can be interfaced(e.g., either mechanically or electrically) with at least one opticalelement of the optical assembly 620. Then, the multifocal block 640 maybe configured to adjust focus of the image light emitted from thedisplay 630 and propagated through the optical assembly 620 by adjustingan optical position of the at least one optical element of the opticalassembly 620, based on the determined eye tracking information obtainedfrom the eye tracking system 635. By adjusting the optical position, themultifocal block 640 varies focus of the image light propagated throughthe optical assembly 620 towards the user's eye. The multifocal block640 may be also configured to adjust resolution of the image lightemitted by the display 630 by performing foveated rendering of the imagelight, based at least in part on the determined eye tracking informationobtained from the eye tracking system 635. In this case, the multifocalblock 640 provides appropriate image signals to the display 630. Themultifocal block 640 provides image signals with a maximum pixel densityfor the display 630 only in a foveal region of the user's eye-gaze,while providing image signals with lower pixel densities in otherregions.

The I/O interface 615 is a device that allows a user to send actionrequests and receive responses from the console 605. An action requestis a request to perform a particular action. For example, an actionrequest may be an instruction to start or end capture of image or videodata or an instruction to perform a particular action within anapplication. The I/O interface 615 may include one or more inputdevices. Example input devices include: a keyboard, a mouse, a gamecontroller, or any other suitable device for receiving action requestsand communicating the action requests to the console 605. An actionrequest received by the I/O interface 615 is communicated to the console605, which performs an action corresponding to the action request. Insome embodiments, the I/O interface 615 includes an IMU 615 thatcaptures calibration data indicating an estimated position of the I/Ointerface 615 relative to an initial position of the I/O interface 615.In some embodiments, the I/O interface 615 may provide haptic feedbackto the user in accordance with instructions received from the console605. For example, haptic feedback is provided when an action request isreceived, or the console 605 communicates instructions to the I/Ointerface 615 causing the I/O interface 615 to generate haptic feedbackwhen the console 605 performs an action.

The console 605 provides content to the NED 610 for processing inaccordance with information received from one or more of: the DCA 625,the NED 610, and the I/O interface 615. In the example shown in FIG. 6,the console 605 includes an application store 650, a tracking module655, and an engine 645. Some embodiments of the console 605 havedifferent modules or components than those described in conjunction withFIG. 6. Similarly, the functions further described below may bedistributed among components of the console 605 in a different mannerthan described in conjunction with FIG. 6.

The application store 650 stores one or more applications for executionby the console 605. An application is a group of instructions, that whenexecuted by a processor, generates content for presentation to the user.Content generated by an application may be in response to inputsreceived from the user via movement of the NED 610 or the I/O interface615. Examples of applications include: gaming applications, conferencingapplications, video playback applications, or other suitableapplications.

The tracking module 655 calibrates the NED system 600 using one or morecalibration parameters and may adjust one or more calibration parametersto reduce error in determination of the position of the NED 610 or ofthe I/O interface 615. For example, the tracking module 655 communicatesa calibration parameter to the DCA 625 to adjust the focus of the DCA625 to more accurately determine positions of structured light elementscaptured by the DCA 625. Calibration performed by the tracking module655 also accounts for information received from an inertial measurementunity (IMU) in the NED 610 and/or an IMU included in the I/O interface615. The IMU is an electronic device that generates data indicating aposition of NED 610 based on measurement signals received one or moreposition sensors associated with the NED 610. Here, the one or moreposition sensors associated with the NED 610 generate one or moremeasurement signals in response to the motion of the NED 505. Examplesof position sensors include one or more accelerometers, one or moregyroscopes, one or more magnetometers, another suitable type of sensorthat detects motion, a type of sensor used for error correction, or somecombination thereof. The one or more position sensors may be locatedexternal or internal to the IMU. Additionally, if tracking of the NED610 is lost (e.g., the DCA 625 loses line of sight of at least athreshold number of structured light elements), the tracking module 655may re-calibrate some or all of the NED system 600.

The tracking module 655 tracks movements of the NED 610 or of the I/Ointerface 615 using information from the DCA 625, the one or moreposition sensors 716, the IMU or some combination thereof. For example,the tracking module 655 determines a position of a reference point ofthe NED 610 in a mapping of a local area based on information from theNED 610. The tracking module 655 may also determine positions of thereference point of the NED 610 or a reference point of the I/O interface615 using data indicating a position of the NED 610 from the IMU orusing data indicating a position of the I/O interface 615 from an IMUincluded in the I/O interface 615, respectively. Additionally, in someembodiments, the tracking module 655 may use portions of data indicatinga position or the NED 610 from the IMU as well as representations of thelocal area from the DCA 625 to predict a future location of the NED 610.The tracking module 655 provides the estimated or predicted futureposition of the NED 610 or the I/O interface 615 to the engine 645.

The engine 645 generates a three-dimensional mapping of the areasurrounding the NED 610 (i.e., the “local area”) based on informationreceived from the NED 610. In some embodiments, the engine 645determines depth information for the three-dimensional mapping of thelocal area based on information received from the DCA 625 that isrelevant for techniques used in computing depth. The engine 645 maycalculate depth information using one or more techniques in computingdepth from the portion of the reflected light detected by the DCA 625,such as the stereo based techniques, the structured light illuminationtechnique, and the time-of-flight technique. In various embodiments, theengine 645 uses the depth information to, e.g., update a model of thelocal area, and generate content based in part on the updated model.

The engine 645 also executes applications within the NED system 600 andreceives position information, acceleration information, velocityinformation, predicted future positions, or some combination thereof, ofthe NED 610 from the tracking module 655. Based on the receivedinformation, the engine 645 determines content to provide to the NED 610for presentation to the user. For example, if the received informationindicates that the user has looked to the left, the engine 645 generatescontent for the NED 610 that mirrors the user's movement in a virtualenvironment or in an environment augmenting the local area withadditional content. Additionally, the engine 645 performs an actionwithin an application executing on the console 605 in response to anaction request received from the I/O interface 615 and provides feedbackto the user that the action was performed. The provided feedback may bevisual or audible feedback via the NED 610 or haptic feedback via theI/O interface 615.

In some embodiments, based on the eye tracking information (e.g.,orientation of the user's eye) received from the eye tracking system635, the engine 645 determines resolution of the content provided to theNED 610 for presentation to the user on the display 630. The engine 645may be configured to adjust resolution of the content provided to theNED 610 by performing foveated rendering of the presented content, basedat least in part on the determined eye tracking information obtainedfrom the eye tracking system 635. The engine 645 provides the content tothe NED 610 having a maximum resolution on the display 630 in a fovealregion of the user's gaze, whereas the engine 645 provides a lowerresolution in other regions, thus achieving less power consumption atthe NED 610 and saving computing cycles of the console 605 withoutcompromising a visual experience of the user. In some embodiments, theengine 645 can further use the eye tracking information to adjust focusof the image light emitted from the display 630 to prevent thevergence-accommodation conflict. In still other embodiments, the engine645 may determine a distance between an object in the local areaassociated with the NED 610 and a tracked position of the user's eyedetermined by the eye tracking system 635 and instruct one or more ofthe display 630 and the multifocal block 640 to render text images ofvideos at a focal distance associated with the object being imaged. Thatis, the engine 645 may be configured to render virtual objects such thatthey appear to be in the local area from the user's point of view.

The engine 645 may be configured to generate one or more emissioninstructions (e.g., via a controller associated with the NED 610). Thegenerated emission instructions include information about a level ofvoltage applied to a stacked LC structure (e.g., one of stacked LCstructures 300, 400, and 500) associated with NED 610. Responsive to thelevel of voltage in the emission instructions, the engine 645 modulatesthe image light propagating through the multifocal block 640. In variousembodiments, the engine 645 determines 610 that a failure has occurredin one of the stacked LC structures (e.g., one of the stacked LCstructures 300, 400, and 500. Determining that a failure has occurredcomprises determining that the intensity of a ghost image is above athreshold value. In some embodiments, determining that a failure hasoccurred comprises that the light output by a stacked LC structure doesnot have the appropriate polarization. In still other embodiments,determining that a failure has occurred comprises an input from a userthe NED 610. In one or more embodiments, determining that the intensityof a ghost image is above a threshold value utilizes a camera associatedwith a controller associated with the NED 610; and determining that thelight output by a stacked LC structure is not the appropriatepolarization comprises the use of a camera and one or more polarizers.Responsive to determining that a failure has occurred, the engine 645may generate instructions identifying the driving LC cell (e.g., LC cell305 a-b, 405 a-b, and 505 a-b) driving a stacked LC structure. In one ormore embodiment, instructions comprise a voltage value provided by acontroller associated with the NED 610 based on one or more instructionsfrom the engine 645.

Specific Design Examples

Below various specific design examples of stacked LC structures arediscussed. The examples below discuss different configurations ofstacked LC structures that each provide, broadband switching (e.g., 450nm-650 nm) of circularly polarized light for a large FOV. The designexamples discussed herein enable board-band and broad angularpolarization rotators. Additionally, in each of the embodimentsdiscussed below in conjunction with FIGS. 7-10, the total phaseretardation of the stacked LC structure is controllable through theapplication of a voltage to one of the optically transparent andelectrically conductive substrates. That is, the stacked LC structuresdiscussed below in conjunction with FIGS. 7-10 may additionally oralternatively be configured as a switchable waveplate responsive to anapplied voltage. Here, total phase retardation of the stacked LCstructures may be equivalent to that of a quarter waveplate, a halfwaveplate, and a full waveplate.

The geometric shape of the stacked LC structures is similar to that ofcommon prescription lenses. For example, geometric shapes embodied bythe LC structures discussed herein may be one of a square shape, a roundshape, a triangular shape, an oblong shape, an oval shape, a diamondshape, and a heart shape. Thus, in an embodiment, the LC structures maybe manufactured to match shape of the user's face. We note that thedesigns discussed herein are may include Pancharatnam Berry Phase (PBP)liquid crystal lenses and as well as any optical element associated withlinearly or circularly polarized light (e.g., lenses, gratings,polarizers, rotators, and waveplates). PBP liquid crystal lenses aredescribed in U.S. application Ser. No. 15/693,846, filed Sep. 1, 2017,which is incorporated by reference in its entirety herein.

In some embodiments, the stacked LC structures described herein may beconfigured into one of two states based on an applied voltage value by,for example, a controller. The controller is configured to apply a firstvoltage value and a second voltage value wherein the first voltage valueis lower than the second voltage value. For example, the first voltagevalue is 0 volts (V) and the second voltage value is 9 V. In variousembodiments, a frame rate of the stacked LC structure is dependent uponthe applied voltage.

It is important to note that these designs are merely illustrative, andother designs of stacked LC structures may be generated using theprinciples described herein.

FIG. 7 is an isometric view of a stacked LC structure 700 comprising twoLC cells in a twist angle configuration, in accordance with anembodiment. The stacked LC structure 700 additionally includes foursubstrates 710 a, 710 b, 710 c, and 710 d. Here, the LC cell 720 a isbetween substrate 710 a and substrate 710 b and LC cell 720 b is betweensubstrate 710 c and substrate 710 d. In FIG. 7, light 740 is incident onsubstrate 710 a and propagates through the stacked LC structure 700 viathe substrate 710 a, LC cell 720 a, substrate 710 b, substrate 710 c, LCcell 720 b, and substrate 710 d. The light 740 exits the stacked LCstructure 700 via the substrate 710 d as light 750. The substrates 710a-d are optically isotropic and are configured to apply a uniformelectric field through a LC cell (e.g., one of LC cell 720 a or LC cell720 b) in response to an applied voltage. For example, each of thesubstrates 710 a-d are comprised of a glass, or a plastic materialcoated with an optically transparent film type electrode (i.e., ITO).The substrates 710 a, 710 b, 710 c, and 710 d are each an embodiment ofany one of the bottom substrates 310 a-b, 410 a-b, and 510 a-b or thetop substrates 330 a-b, 430 a-b, and 530 a-b which are discussed, above,in conjunction with FIGS. 3A-B, 4A-B, and 5A-B. The LC cells 720 a-b areembodiments any one of the LC cells 305 a-b which are discussed, above,in conjunction with FIGS. 3A-B, 4A-B, and 5A-B.

In the example embodiments depicted, below, the LC cell 720 a and LCcell 720 b are both sensitive to an applied electric field and comprisea plurality of LC molecules (e.g., a plurality of LC molecules 320).Each of the plurality of LC molecules is a centrosymmetric nanocrystaland exhibits a size and shape dependent dipole moment. In someembodiments, each of the plurality of LC molecules is a Zinc Sulfide(ZnS) and/or Lead Sulfide (PbS) nanorod encapsulated in a liquidcrystalline medium. Here, the LC cell 720 a and LC cell 720 b areconfigured to cause a phase adjustment in the polarization of the light740 by a first amount and a second amount, respectively. In thisdiscussion it is assumed that the light 740 is RCP.

The light 750 is light 740 whose polarization is changed by a thirdamount of phase adjustment, representative of the total phase adjustmentcaused by the stacked LC structure 700. And the total amount of phaseadjustment is such that polarization of light 750 may be rotatedrelative to the light 740. For example, the light 750 is RCP while thelight 740 is LCP. In other example embodiments, the light 750 is RCP,LCP, horizontally linearly polarized, vertically lineally polarized, orany combination thereof. The orientation of the LC cell 720 a relativeto the LC cell 720 b is such that birefringence of the LC cell 720 bcompensates for any ghost image introduced to the light 740 passingthrough the LC cell 720 a. And compensation may be such that the ghostimage is mitigated or, in some cases, removed entirely from the light750 exiting the stacked LC structure 700.

In an embodiment, the stacked LC structure 700 has a first state and asecond state. In various embodiments, a state of the stacked LCstructure 700 is controllable via the application of a control voltage.In an embodiment, a first voltage value configures the stacked LCstructure 700 into the first state and a second voltage value configuresthe stacked LC structure 700 a second state. In an embodiment, in thefirst state, the stacked LC structure 700 polarizes an input RCP light(e.g., light 740) at wavelengths 650 nm, 550 nm, and 450 nm and inputangles from −60° to 60°. For example, in a first state, the input light(e.g., light 740) is RCP and the output light (e.g., light 750) is LCPover incident polar angles from −60° to 60°. In the second state, thestacked LC structure 700 does not modify the polarization of an inputlight. In an example embodiment, a LC stacked structure 700 operates ina first state under the applied of a first value is applied, and the LCstacked structure 700 operates in a second state when a voltage of asecond value is applied.

FIG. 8 is an isometric view of a stacked LC structure 800 comprising twoLC cells (e.g., LC cell 720 a and LC cell 720 b) in a twisted nematicconfiguration biaxial compensation films (e.g., biaxial compensationfilm 830 a, biaxial compensation film 830 b, and biaxial compensationfilm 830 c), in accordance with an embodiment. The biaxial compensationfilms 830 a-d are optical components with a specific angularbirefringence configured to compensate the angular dependence of LCcells. In the example, embodiment of FIG. 8, the biaxial compensationfilms are aligned such that their birefringence is offset from oneanother by 90°. In various embodiments, the biaxial compensation films830 a, 830 b, 830 c, and 830 d are plastic with a birefringence alongits optical axis. In the example embodiment associated with FIG. 8 theoptical axis of the biaxial compensation films 830 c and the biaxialcompensation films 830 d are oriented such that the optical axis of oneis orthogonal to that of the other. That is, in an example embodiment ifthe birefringence of the biaxial compensation film is 830 c isorientated along the X axis, then the birefringence of the biaxialcompensation film 830 d is orientated along the Y axis or the Z axis. Inan embodiment, each of the biaxial compensation films 830 a, 830 b, 830c, and 830 d are comprised of poly-propylene which is extruded andstretched in two directions (e.g., along the X and Z axis). The stackedLC structure 800 also includes substrates 710 a-d. The substrates 710a-d are further described in detail, above, in conjunction with FIG. 7.

In FIG. 8, the LC cell 720 a is between substrate 710 a and substrate710 b and LC cell 720 b is between substrate 710 c and substrate 710 d.In FIG. 8, light 840 is incident on biaxial compensation film 830 a andpropagates through the stacked LC structure 800. The light 840 exits thestacked LC structure 800 as a light 850 via biaxial compensation film830 d after propagating though substrate 710 a, LC cell 720 a, substrate710 b, biaxial compensation film 830 b, biaxial compensation film 830 c,substrate 710 c, LC cell 720 b, substrate 710 d, and biaxial film 830 d.

The light 850 is light 840 whose polarization is changed by an amount ofphase adjustment, representative of the total phase adjustment caused bythe stacked LC structure 800. And the total amount of phase adjustmentis such that polarization of light 850 may be rotated relative to thelight 840. For example, the light 850 is RCP while the light 840 is LCP.In other example embodiments, the light 850 is RCP, LCP, horizontallylinearly polarized, vertically lineally polarized, or any combinationthereof. The orientation of the LC cell 720 a relative to the LC cell720 b is such that birefringence of the LC cell 720 b compensates forany ghost image introduced to the light 840 passing through the LC cell720 a. And compensation may be such that the ghost image is mitigatedor, in some cases, removed entirely from the light 850 exiting thestacked LC structure 800.

In an embodiment, the stacked LC structure 800 has a first state and asecond state. In various embodiments, a state of the stacked LCstructure 800 is controllable via the application of a control voltage.In an embodiment, a first voltage value configures the stacked LCstructure 800 into the first state and a second voltage value configuresthe stacked LC structure 800 a second state. In some embodiments, in theinput light (e.g., light 840) is RCP. In the first state, the stacked LCstructure 800 polarizes input RCP light at wavelengths 650 nm, 550 nm,and 450 nm and input polar angles from −60° to 60°. In the second state,a RCP input light is converted into RCP output light at wavelengths 650nm, 550 nm, and 450 nm and at input polar angles from −25° to 25°. Inother words, the stacked LC structure 800 does not modify thepolarization of input RCP polarized light in the second state. In anexample embodiment, a LC stacked structure 800 operates in a first stateunder the applied of a first value is applied, and the LC stackedstructure 800 operates in a second state when a voltage of a secondvalue is applied.

FIG. 9 is an isometric view of a stacked LC structure 900 comprising twoLC cells (e.g., LC cell 720 a and LC cell 720b) in a twisted nematicconfiguration and includes plastic film substrates, in accordance withan embodiment. The LC cell 720 a is between biaxial compensation film930 a and biaxial compensation film 930 b. The LC cell 720 b is betweenbiaxial compensation film 930 c and biaxial compensation film 930 d. InFIG. 9A, light 940 is incident on biaxial compensation film 930 a andpropagates through the stacked LC structure 900 via the biaxialcompensation film 930 a. The light 940 exits the stacked LC structure asa light 950 via biaxial compensation film 930 d after propagatingthrough LC cell 720 a, biaxial compensation film 930 b, biaxialcompensation film 930 c, LC cell 720 b, and biaxial compensation film930 d. Here, biaxial compensation films 930 a, 930 b, 930 c, and 930 dare embodiments of biaxial compensation films 830 a, 830 b, 830 c, and830 d described above in conjunction with FIG. 8.

The light 950 is light 940 whose polarization is changed by an amount ofphase adjustment, representative of the total phase adjustment caused bythe stacked LC structure 900. And the total amount of phase adjustmentis such that polarization of light 950 may be rotated relative to thelight 940. For example, the light 950 is RCP while the light 940 is LCP.In other example embodiments, the light 950 is RCP, LCP, horizontallylinearly polarized, vertically lineally polarized, or any combinationthereof. The orientation of the LC cell 720 a relative to the LC cell720 b is such that birefringence of the LC cell 720 b compensates forany ghost image introduced to the light 940 passing through the LC cell720 a. And compensation may be such that the ghost image is mitigatedor, in some cases, removed entirely from the light 950 exiting thestacked LC structure 900.

In an embodiment, the stacked LC structure 900 has a first state and asecond state. In various embodiments, a state of the stacked LCstructure 900 is controllable via the application of a control voltage.In an example embodiment, in the first state, the input light (e.g.,light 940) is RCP and the output light (e.g., light 950) is LCP. Forexample, in the first state, the stacked LC structure 900 polarizesinput RCP light at wavelengths 650 nm, 550 nm, and 450 nm and inputpolar angles from −60° to 60°. In some example embodiments, in thesecond state, the input light is RCP and the output light is also RCP(at wavelengths 650 nm, 550 nm, and 450 nm and at input polar anglesfrom −25° to 25°. In other words, the stacked LC structure 900 does notmodify the polarization of input RCP light in the second state. In anexample embodiment, a LC stacked structure 900 operates in a first stateunder the applied of a first value is applied, and the LC stackedstructure 900 operates in a second state when a voltage of a secondvalue is applied.

FIG. 10 is an isometric view of a stacked LC structure 1000 comprisingtwo LC cells (e.g., LC cell 720 a and LC cell 720 b) in a twistednematic configuration with plastic film substrates and compensated withbiaxial compensation films, in accordance with an embodiment. The LCcell 720 a is between a biaxial compensation film 930 a and biaxialcompensation film 930 b and LC cell 720 b is between biaxialcompensation film 930 c and biaxial compensation film 930 d. In FIG.10A, light 1040 is incident on biaxial compensation film 1030 a andpropagates through the stacked LC structure 1000 via the biaxialcompensation film 930 a. The light 1040 exits the stacked LC structure1000 as a light 1050 via biaxial compensation film 1030 d afterpropagating through biaxial compensation film 930 a, LC cell 720 a,biaxial compensation film 930 b, biaxial compensation film 1030 b,biaxial compensation film 1030 c, biaxial compensation film 930 c, LCcell 720 b, biaxial compensation film 930 d, and biaxial compensationfilm 1030 d. Here, the biaxial compensation film 1030 a, 1030 b, 1030 c,and 1030 d are embodiments of biaxial compensation films 830 a, 830 b,830 c, and 830 d described above in conjunction with FIG. 8.

The light 1050 is light 1040 whose polarization is changed by an amountof phase adjustment, representative of the total phase adjustment causedby the stacked LC structure 1000. And the total amount of phaseadjustment is such that polarization of light 1050 may be rotatedrelative to the light 1040. For example, the light 1050 is RCP while thelight 1040 is LCP. In other example embodiments, the light 1050 is RCP,LCP, horizontally linearly polarized, vertically lineally polarized, orany combination thereof.

In an embodiment, the stacked LC structure 1000 has a first state and asecond state. In various embodiments, a state of the stacked LCstructure 1000 is controllable via the application of a control voltage.In some embodiments, in the first state, the input light (e.g., light1040) is RCP and the output light (e.g., light 1050) is LCP. Forexample, in the first state, a RCP input light is converted into LCPoutput light at wavelengths 650 nm, 550 nm, and 450 nm and at inputpolar angles from −60° to 60°. In some example embodiments, in thesecond state, a RCP input light is converted into RCP output light atwavelengths 650 nm, 550 nm, and 450 nm and at input polar angles from−35° to 40°. In other words, the stacked LC structure 1000 does notmodify the polarization of input RCP polarized light in the secondstate. In an example embodiment, a LC stacked structure 10000 operatesin a first state under the applied of a first value is applied, and theLC stacked structure 1000 operates in a second state when a voltage of asecond value is applied.

Additional Configuration Information

The foregoing description of the embodiments of the disclosure have beenpresented for the purpose of illustration; it is not intended to beexhaustive or to limit the disclosure to the precise forms disclosed.Persons skilled in the relevant art can appreciate that manymodifications and variations are possible in light of the abovedisclosure.

Some portions of this description describe the embodiments of thedisclosure in terms of algorithms and symbolic representations ofoperations on information. These algorithmic descriptions andrepresentations are commonly used by those skilled in the dataprocessing arts to convey the substance of their work effectively toothers skilled in the art. These operations, while describedfunctionally, computationally, or logically, are understood to beimplemented by computer programs or equivalent electrical circuits,microcode, or the like. Furthermore, it has also proven convenient attimes, to refer to these arrangements of operations as modules, withoutloss of generality. The described operations and their associatedmodules may be embodied in software, firmware, hardware, or anycombinations thereof.

Any of the steps, operations, or processes described herein may beperformed or implemented with one or more hardware or software modules,alone or in combination with other devices. In one embodiment, asoftware module is implemented with a computer program productcomprising a computer-readable medium containing computer program code,which can be executed by a computer processor for performing any or allof the steps, operations, or processes described.

Embodiments of the disclosure may also relate to an apparatus forperforming the operations herein. This apparatus may be speciallyconstructed for the required purposes, and/or it may comprise ageneral-purpose computing device selectively activated or reconfiguredby a computer program stored in the computer. Such a computer programmay be stored in a nontransitory, tangible computer readable storagemedium, or any type of media suitable for storing electronicinstructions, which may be coupled to a computer system bus.Furthermore, any computing systems referred to in the specification mayinclude a single processor or may be architectures employing multipleprocessor designs for increased computing capability.

Embodiments of the disclosure may also relate to a product that isproduced by a computing process described herein. Such a product maycomprise information resulting from a computing process, where theinformation is stored on a nontransitory, tangible computer readablestorage medium and may include any embodiment of a computer programproduct or other data combination described herein.

Finally, the language used in the specification has been principallyselected for readability and instructional purposes, and it may not havebeen selected to delineate or circumscribe the inventive subject matter.It is therefore intended that the scope of the disclosure be limited notby this detailed description, but rather by any claims that issue on anapplication based hereon. Accordingly, the disclosure of the embodimentsis intended to be illustrative, but not limiting, of the scope of thedisclosure, which is set forth in the following claims.

1. A stacked liquid crystal (LC) structure comprising: a plurality of LCcells configured to rotate a polarization of a broadband light over arange of wavelengths and a range of incident angles, the plurality of LCcells are arranged in a stack such that the broadband light passesthrough each of the plurality of LC cells consecutively, wherein anamount of phase adjustment caused by the plurality of LC cells stack iswavelength independent over the range of wavelengths and the range ofincident angles and the plurality of LC cells are oriented relative toeach other such that a cumulative rotation of the polarization for allbands of light within the broadband light is from a first polarizationto a second polarization.
 2. The stacked LC structure of claim 1 whereinthe stacked LC structure is associated with a head mounted display(HMD).
 3. The stacked LC structure of claim 1 further comprising a firststate and a second state wherein in the first state the stacked LCstructure changes a polarization state of the incident broadband lightfrom a first polarization state to the second polarization state and ina second state the stacked LC structure maintains the polarization stateof incident light.
 4. The stacked LC structure of claim 3, wherein thefirst state is associated with a first voltage value and the secondstate is associated with a second voltage value.
 5. The stacked LCstructure of claim 4, wherein a framerate of the stacked LC structure isdependent on the magnitude of the applied voltage.
 6. The stacked LCstructure of claim 1, wherein an optical mode of the stacked LCstructure is selected from a group consisting of: an electricalcontrolled birefringence (ECB) mode , a vertical aligned (VA) mode), amultiple-domain vertical aligned (MVA) mode, a twisted nematic (TN)mode, a super twisted nematic (STN) mode, and an optical compensated(OCB) mode.
 7. The stacked LC structure of claim 1, wherein at least oneof the plurality of LC cells is a nematic LC cell, a nematic LC cellwith chiral dopants, a chiral LC cell, a uniform lying helix (ULH) LCcell, a ferroelectric LC, or an electrically drivable birefringencematerials.
 8. The stacked LC structure of claim 1, wherein the stackedLC cell comprises: a first top substrate, a first bottom substrate, asecond top substrate, and a second bottom substrate configured toreceive broadband light and couple it into one of a first LC cell and asecond LC cell; and wherein the first LC cell and the second LC cell areconfigured to perform a phase adjustment to the polarization of thereceived broadband light in a broad incident angle.
 9. The stacked LCstructure of claim 8, wherein the first top substrate, the second topsubstrate, the first bottom substrate, and the second bottom substrateare each electrically conductive and optically transparent.
 10. Thestacked LC structure of claim 8, wherein the first top substrate and thefirst bottom substrate are further configured to apply an electric fieldacross the first LC cell.
 11. The stacked LC structure of claim 8,wherein the stacked LC structure further includes a compensation layer,wherein the compensation layer increases the range of wavelengths overwhich the amount of phase adjustment caused by the plurality of LC cellsis wavelength independent.
 12. The stacked LC structure of claim 11,wherein the compensation layer is a multi-layer birefringence film. 13.The stacked LC structure of claim 1, wherein the stacked LC structure isa switchable waveplate with a total phase retardation that iscontrollable through the application of an external voltage to one of afirst LC cell and a second LC cell of the plurality of LC cells.
 14. Thestacked LC structure of claim 13, wherein the stacked LC structure isone of a quarter waveplate, a half waveplate, and a full waveplate. 15.The stacked LC structure of claim 1, wherein a field of view of thestacked LC structure is at least 60 degrees.
 16. A stacked liquidcrystal (LC) structure associated with a head mounted display, thestacked LC structure comprising: a plurality of LC cells configured torotate a polarization of a broadband light over a range of wavelengthsand a range of incident angles d incident angle, the plurality of LCcells are arranged in a stack such that the broadband light passesthrough each of the plurality of LC cells consecutively, wherein anamount of phase adjustment caused by each LC cell in the plurality of LCcells is wavelength independent over the range of wavelengths and therange of incident angles and the plurality of LC cells are orientedrelative to each other such that a cumulative rotation of thepolarization for all bands of light within the broadband light is from afirst polarization to a second polarization; and a controller configuredto: determine that a failure has occurred in a first LC cell, and applya voltage to a second LC cell in order to drive the stacked LCstructure.
 17. The stacked LC structure of claim 16, wherein each of thestacked LC cell comprises: a first top substrate, a first bottomsubstrate, a second top substrate, and a second bottom substrateconfigured to receive broadband light and couple it into one of thefirst LC cell and the second LC cell; and wherein the first LC cell andthe second LC cell are configured to perform a phase adjustment to thereceived broadband light.
 18. The stacked LC structure of claim 17,wherein the first top substrate, the second top substrate, the firstbottom substrate, and the second bottom substrate are each electricallyconductive and optically transparent.
 19. The stacked LC structure ofclaim 17, wherein the first top substrate and the first bottom substrateare further configured to apply an electric field across the first LCcell.
 20. The stacked LC structure of claim 17, wherein the stacked LCstructure further includes a compensation layer, wherein thecompensation layer increases the range of wavelengths over which theamount of phase adjustment caused by the plurality of LC cells iswavelength independent.